Question

I want to use a QueueSender in a multi-threaded environment.

Is QueueSender.send() thread safe?

Answer 1

No, a MessageProducer/QueueSender is not thread safe.

Or more specifically: The Session is not thread safe. The JavaDoc for Session explicitly mentions this in its first sentence:

A Session object is a single-threaded context for producing and consuming messages.

And since a MessageProducer/QueueSender is bound to a Session you must not use it from more than one thread at the same time. In fact you must not use it from two different threads at different times either!